1. Field of the Invention
The present invention generally relates to digital communication systems and, more particularly, to an implementation of an advanced mobile phone service (AMPS) compatible analog channel unit on a digital cellular, time division multiplex/time division multiple access (TDM/TDMA) hardware platform conforming Electronic Industries Association (EIA) standard EIA/IS-54B hardware platform.
2. Description of the Prior Art
Advanced mobile phone service (AMPS) is term coined by what was then the Bell System for a cellular mobile-radio system. The basic idea was to divide transmission areas into "cells" to handle radio traffic. The January 1979 issue of The Bell System Technical Journal, vol. 58, no. 1, was devoted entirely to AMPS. Cellular mobile telephone systems are now widely installed in many metropolitan areas throughout the United States. As described in The Bell System Technical Journal, the service area covered by a cellular system is divided into a number of cells, each having a base station which can effect a telephone connection to any mobile unit located in the cell. The base stations are all connected to and controlled by a central mobile telephone switching office (MTSO) that connects to the telephone network. For additional background on cellular mobile telephone systems, the reader is referred to the textbook by William C. Y. Lee entitled Mobile Cellular Telecommunications Systems, McGraw-Hill (1989).
Current cellular systems are analog systems using conventional hardware and analog modulation techniques. There is now an effort to convert many cellular systems to digital systems using digital hardware and digital modulation techniques. There are many advantages to such a conversion, not the least of which is a substantial increase in the number of channels which can be handled within a given frequency allocation. There is, however, a substantial installed base of analog subscribers requiring a transition from analog service to digital service, during which time both analog and digital service must be provided.
Most base station manufacturers provide analog service through analog channel units. In these channel units, functions are implemented using a hardware intensive but now well established approach. This allows the analog channel unit to be manufactured at a lower cost; however, conversion to digital service requires a change in the system hardware accompanied by additional capital expense to the service provider.